Purchasable hardware wallets

The private keys generated by the device never leave it and cannot be accessed by a malware. Thanks to a limited USB protocol only a payment template can be sent into the device (address and amount) which then has to be confirmed by a physical user interaction (visual verification of the transaction details and pressing the confirmation button).

TREZOR uses a deterministic wallet structure which means it can hold an unlimited number of keys (BIP32).

A recovery seed is generated when the device is initialized. In case it gets lost or stolen, all it's contents can be recovered using the seed (private keys, bitcoin balance and transaction history) into a new device or another BIP39 compatible wallet.

TREZOR introduced a unique way of PIN entering preventing keyloggers from recording it even when entered on a compromised computer.

An encryption passphrase can be set on top of the PIN protection. More passphrases can be used for plausible deniability.

Not purchasable hardware wallets

BitcoinCard Megion Technologies-Card based wallet

Incorporates a e-paper display, keypad, and radio (custom ISM band protocol.) Unfortunately it is fairly limited in terms of transaction I/O, requiring a radio gateway or another bitcoincard wherever funds need to be transferred.

BTChip btchip USB based transaction signer and private key holder

USB smartcard dedicated to bitcoins, no keypad or display so trust in the host device is required. An improvement has been implemented that uses a secret value known to the user during the transaction for additional security.